1. Field
This invention comprises a wastewater treatment method employing chemical/mechanical dewatering and biological treatment technology for first propagating and recovering of photo biomass/algae to reduce BOD's and heavy metals to produce recovered treated wastewater suitable for reuse.
2. State of the Art
Various types of wastewaters are known. As used herein, it is principally directed to wastewaters containing organic and macronutrients suitable for growth of plants, algae, and photo biomass, including runoff from farmlands, domestic sewage from dwellings, business buildings, institutions, containing ground water, surface water, and/or storm water, and can include wastewater, having already undergone primary and secondary treatment according to conventional wastewater treatment plant processes. Consequently wastewater as used herein also includes other agricultural and industrial wastewaters containing similar nutrients and requiring similar conditioning, disinfection, and deodorizing to provide feedstock for growing photo biomass/algae. One source of wastewater is that present in sewage treatment gathering systems, which are processed by various methods. Most large municipal systems employ a series of settling ponds sequentially concentrating the solids contained in wastewater either with or without polymers for separation from liquids via mechanical separation means, such as belt presses. To produce a clean effluent that can be safely discharged to watercourses, wastewater treatment operations use three or four distinct stages of treatment to remove harmful contaminants; according to the United Nations Environmental Programme Division of Technology, Industry, and Economics Newsletter and Technical Publications Freshwater Management Series No. 1, “Bio-solids Management: An Environmentally Sound Approach for Managing Sewage Treatment Plant Sludge”. 
Preliminary wastewater treatment usually involves gravity sedimentation of screened wastewater to remove settled solids. Half of the solids suspended in wastewater are removed through primary treatment. The residual material from this process is a concentrated suspension called primary sludge, subsequently undergoing additional treatment to become bio-solids.
Secondary wastewater treatment is accomplished through a biological process, removing biodegradable material. This treatment process uses microorganisms to consume dissolved and suspended organic matter, producing carbon dioxide and other by-products. The organic matter benefits by providing nutrients needed to sustain the communities of microorganisms. As microorganisms feed, their density increases and they settle to the bottom of processing tanks, separated from the clarified water as a concentrated suspension called secondary sludge, biological sludge, waste activated sludge, or trickling filter humus. By breaking down the sludge, the wastewater system loses energy and increases carbon dioxide emissions.
Tertiary or advanced treatment is used when extremely high-quality effluent is required, including direct discharge to a drinking water source. The solid residual collected through tertiary treatment consists mainly of chemicals added to clean the final effluent, which are reclaimed before discharge, and therefore not incorporated into bio-solids. Tertiary or advanced treatment does not reduce the treated wastewater brine content, requiring energy intensive Quaternary brine treatment removal using reverse osmosis and distillation, and other methods.
Combined primary and secondary solids comprise the majority of material used at municipal plants for bio-solids production. Careful management throughout the entire treatment process allows plant operators to control the solids content, nutrient value and other constituents of bio-solids.